Two projects are proposed. Both are concerned with the choice of transmitters in neurons derived from the neural crest (sympathetic principal neurons and primary sensory neurons), and both will use a microculture procedure which permits application of electrophysiological and morphological techniques to the same neuron. Project I. Dissociated sympathetic principal neurons will be obtained from the superior cervical ganglia, or other ganglia, of newborn rats or rats at various ages up to fully adult. Transmitter status will be determined by assay against cardiac myocytes or other peripheral target cells, with special attention to the control of the choice of norepinephrine and acetylcholine as transmitters. Transitions in status will be followed with serial assays of individual neurons. Project II. Primary sensory neurons derived from the nodose, trigeminal or dorsal root ganglia will be co-cultured with smooth muscle cells of the irideal sphincter. Special emphasis will be given to neurons which contain Substance P-like immunoreactivity.